Damon Lindelof has long maintained that his “Watchmen” is neither a direct adaptation nor a reboot of the original comic book series created by Alan Moore and Dave Gibbons. Instead, the showrunner has described his HBO series, which premiered Oct. 20, as more of a “remix,” albeit one that treats the 12-issue comic as canon: The new series does not alter any of the events that happen in its source material. Here’s what you need to know:

What to know if you’ve read the comics

The TV series is set in the same world introduced in the comics. All the things that happened in the 1985-set comics are historical events within the 2019-set show. This means it has been more than 30 years since the fake alien squid attack that destroyed New York and saved the world from nuclear annihilation.

A couple of characters will be familiar, including Laurie Jupiter (played by Jean Smart) and Adrian Veidt, aka Ozymandias (Jeremy Irons). Doctor Manhattan makes an appearance, too. Rorschach is still dead, but his legacy lives on in the form of a terrorist white supremacist group that wears his mask. It’s still a world in which being a masked vigilante is illegal, unless you’re working for a government agency like the police in Tulsa, Okla., where most of the series is set.

What to know if you’ve seen the movie

You might not understand the squid jokes. That is to say, the 2009 film adaptation was fairly faithful to the plot of the comic book, except that it exchanged the giant squid ending for a nuclear bomb.

What to know if you know nothing

“Watchmen” is set in an alternate world in which certain historical events played out differently: The rise of superheroes helped the U.S. win the Vietnam War, and Richard Nixon never faced impeachment (he became so popular that the 22nd Amendment was repealed).

Despite the existence of superheroes, most of these individuals did not have superhuman abilities. But by 1977, heroes were so unpopular with the police and the public that they were outlawed. One, Rorschach, is the main holdout among the vigilantes after it becomes illegal. One person who does have powers is Doctor Manhattan. He gained his abilities (and strange appearance) after a lab mishap that tore his atoms apart (he now experiences time in a nonlinear fashion).

In 1985, the super-intelligent Veidt helped de-escalate tensions between the U.S. and Soviet Union by faking that alien squid invasion in New York that killed millions. Among those who knew about Veidt’s actions but chose to keep it a secret for the “greater good” were Laurie (Silk Spectre), Doctor Manhattan and Dan Dreiberg (Nite Owl).

Rorschach, who planned on revealing the truth, was killed by Doctor Manhattan before he left Earth for someplace less complicated.

Got all that?